Vacuum vapor deposition utilizing low voltage electron beam

ABSTRACT

RAPID DEPOSITION RATES AND EFFICIENT MATERIAL UTILIZATION ARE ACHIEVED IN A VACUUM VAPOR DEPOISITION SYSTEM BY A LOW VOLTAGE, HIGH CURRENT ELECTRON BEAM ARRANGEMENT FOR HEATING THE MATERIAL TO A SUFFICIENTLY HIGH TEMPERATURE FOR VAPORIZATION, FOR IONIZING THE VAPORIZED MATERIAL IN ORDER TO IMPART A POSITIVE CHARGE THERETO AND FOR ELECTROSTATICALLY AND/OR ELECTROMAGNETICALLY ATTRACTING THE IONIZED, VAPORIZED MATERIAL TO A SUBSTRATE, AT WHICH DEPOSITION OF THE MATERIAL OCCURS.   D R A W I N G

Feb. 9, v1971 J. Rv MORLEY VACUUM VAPOR KDEPOSITION UTILIZING LOW VOLTAGE ELECTRON BEAM Filed Feb. 23, 1968 ATTORNEY United States Patent O1 3,562,141 VACUUM VAPOR DEPOSITION UTILIZING LOW VOLTAGE ELECTRON BEAM .lohn R. Morley, Rutland St., Carlisle, Mass. 01741 Filed Feb. 23, 1968, Ser. No. 707,863 Int. Cl. C23c .Z5/00 U.S. Cl.. 204-298 5 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND AND SUMMARY OF THE INVENTION The present invention relates to vapor deposition of high melting temperature materials onto substartes and, more particularly, to the deposition of a selected material or alloy onto a selected substrate by heating the material in a substantial vacuum to form a vapor, directing the vapor toward the substrate and condensing the material from the vapor phase onto the substrate. Conventional deposition involves either, resistance, induction or electron beam heating and vaporizing of the material with subsequent ilow of the vapor to the substrate; or sputtering at high potential under vacuum with ultimate condensation of material onto the substr-ate. Such conventional deposition has suffered from various problems. Thus the density of the vapor directed toward the substrate generally spreads out in accordance with the inverse square law so that only a proportion of the material actually impinges on the substrate, the remainder of the material being wasted by deposition on the chamber walls and substrate holder. Also while rapid rates of evaporation and subsequent deposition can be achieved by electron beam, resistance and induction heating methods, both the deposition collection eiciency and the adhesion of the coating to the substrate could be improved. Further, if the temperature and cleanliness of the substrate are not controlled precisely, the deposited coating `will have poor adhesion to the substrate and, in the case of thick deposits, often will crack and flake, Finally in the lcase of sputtering, although strongly adhering lms are produced by ionization of evaporated material and subsequent electrostatic acceleration, the deposition rate is low because the quantity of ions that can be generated and accelerated under sputtering conditions is small.

The primary object of the present invention is to avoid such large waste of material and low rate of evaporation, by vaporizng the material to be deposited, charging a large fraction of the vaporized material to provide positive ions and attracting these positive ions to the substrate by a negative potential. In accordance with the present invention, large quantities of ions ar generated by utilizng a low voltage electron beam while at the same time pro- 'viding a suitable quantity of heat to maintain the evaporating source at the correct temperature. For almost all substances, the number of ions produced per electron is greatest 'when the electrons have energies bet-Ween 50 and 150 volts, consequently it is most desirable to utilize a beam of electrons within this energy range. `Conventional electron beams operate in the kilovolt range where the ionization eciency is several orders of magnitude lower. Fur- 5 electrons (current) 3,562,141 Patented Feb. 9, 1971 ice' ther, to maintain the necessary amount of electron beam power (amps volts) in order to heat and vaporize the source material, it is desirable to increase the current and to reduce the voltage of the beam. By doing this, more pass through the vapor above the source, for a given input power, thus producing more ions. yOne method of producing a low voltage, high current electron beam is by hollow cathode discharge to effect vaporizing and charging in a manner to be described below. It is to be understood that other methods for low voltage high c-urrent electron beam generation also are known and are applicable.

Other objects of the present invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several components and interrelationships, exemplified in the following detailed disclosure, the scope of which will be indicated in the appended claims.

GENERAL DESCRIPTION OF DRAWING For a fuller understanding of the nature and objects of the present invention, reference should be had to the following detailed description, taken in connection with the accompanying drawing, which illustrates an apparatus for material evaporation and ion acceleration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Generally, in order to achieve good efficiency in ionizing material that has been vaporized with an electron beam, the energy of the electrons involved is optimally 'between 50 and 150 electron volts. However, conventional sputtering and conventional electron beam operate typically in the 3 to 30 kilovolt range `and the ionization efciency of these high energy electrons is very low in cornparison to the approximately electron volt energies indicated above to be desirable.

In accordance with the present invention, a low voltage electron beam derived from a hollow cathode discharge unit 10 serves to melt, vaporize and ionize a material 12. As shown, hollow cathode discharge unit 10 includes a water cooled tubular conduit 14 communicating through a suitable valve to a supply of pressurized inert gas 16, such as argon, helium or nitrogen. Mounted on the inner end of tube 14 is a refractory metal tube 18, which serves as a cathode for an electron emission circuit. Cathode 18 is electrically connected to an A C. power supply 20, capable of generating a radio frequency output between cathode 18 and material 12. The cathode itself also is connected to a D C. power source 22, that is variable in the ranges from O to volts and 0 to 1000 amperes. Material 12 is at ground potential. In practice, to establish the discharge between cathode 18 and anode 12, radio frequency power is applied between them, thus causing the gas to ionize and a discharge to be established when the direct current power is applied to the cathode. Ions, being attracted to the cathode, cause it to become heated. When the cathode reaches a temperature at which the work function for electron emission is exceeded, electrons are emitted thermionically from the surface of the cathode. The emitted electrons are accelerated toward the anode material 12 and impinge upon the molecules of gas, which is being introduced through conduit 14 and exhausted as at 15. The gas becomes ionized by the emitted electrons and an ionized discharge is completed to material 12. The discharge, once started, is maintained across the electrical lield between cathode and anode. The radio frequency power then may be deenergized without effect once a steady discharge is established. Further details of hollow cathode discharge units are described in U.S. Pat. No. 3,210,454, issued on Oct. 5, 1965, in the 3 name of John R. Morley for High Temperature Apparatus.

In the illustrated embodiment, hollow cathode discharge unit 10 and material 12 operate within a hermetic chamber 24. Material 12 is contained within a refrectory or water cooled crucible 2S located at the bottom center of chamber 24. Hollow cathode discharge unit 10 projects through a side of chamber 24, being directed horizontally to project its discharge in a trajectory ending at material 12. Associated with hollow cathode discharge unit 10 and crucible 2S, respectively, are beam focusing and bending coils 26 and 28, which are energized by a suitable power supply 30. The ionized vapor from crucible 25 is directed upwardly toward a substrate 32, which is served by a power supply 34 that provides from 0 to 500 volts and from to 500 amperes, negative direct current. A deposited film 36 of material forms on substrate 32, the stream of ionized vapor to the substrate being controlled by deflection plates 38, which in one form are electrostatic and in another form are electromagnetic.

OPERATION In operation, the low voltage high current electron beam from the hollow cathode is generated in the conventional manner but is bent through a 90 angle by shaped magnetic fields generated by coils 26, 2S. The 90 angle is not critical to the successful operation of ythe equipment, and any angle between 0 and 360 may be used to effectuate the same results so long as the path of hollow cathode discharge to the evaporant material and the path of the vapor from the evaporant material to the substrate are different. Typically, the cathode ranges between 50 to 150 volts negative with respect to ground potential, the potential of crucible 25. The hollow cathode beam impinges on material 12, the hollow cathode beam typically having between 100 and 1000 amperes of electrons at 50 to 150 volts. The amount of power is adjustable for the purposes of: heating the material to a suiciently high temperature to achieve vaporization; and ionizing the vapor by passage of the electron beam through the vaporizing material, the ions thus formed being attracted to substrate 32 by the negative potential thereof. Using suitable electrostatic or electromagnetic deflection, as at 38, it is possible to produce predeterminedly non-uniform deposits, as well as uniform deposits.

CONCLUSION The present invention thus provides a vacuum vapor deposition technique for achieving eflicient coating by a low voltage electron beam that vaporizes and ionizes a material to be deposited, for attraction to and deposition on a substrate at predetermined potential. Since certain changes may be made in the foregoing apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the foregoing description or shown in the accompanying draw- 4 ing be interpreted in an illustrative and not in a limiting sense.

What is claimed is:

1. A system for vacuum vapor deposition within a hermetic chamber, said system comprising:

(a) means for evacuating said chamber;

(b) hollow cathode means for generating a low voltage, high current electron beam in the range of to 1000 amperes of electrons at 50 to 150 volts;

(c) means for directingV said beam through a trajectory to an evaporant material, said evaporant material being vaporized 'by said beam, said vaporized material being ionized by said beam through a path, said trajectory and path intersecting, the quantity of ions formed being enhanced by said beam;

(d) means for mounting a substrate to receive said material when ionized through said path; and

(e) means for establishing a potential on said substrate for attracting said ionized material toward said substrate.

2. The vapor deposition means of claim 1 wherein the initial directions of said trajectory' and said path are at an angle to each other.

3. The vapor deposition means of claim 1 wherein deflection means are operatively associated with said path in order to control the movement of material when ionized.

4. The vapor deposition means of claim 1 wherein said electron beam is generated within a plasma incorporating an inert gas and means are provided for continuously exhausting said chamber.

5. The vapor deposition means of claim 1 wherein the quantity of ions formed is enhanced by using said low voltage, high current electron beam, and the probability of producing said ions again increased by the superimposition of a magnetic field generated by coil means in the proximity of the evaporating material.

References Cited UNITED STATES PATENTS 3,428,546 2/1969 Gaum et al 204-298 3,404,084 10/ 1968 Hamilton 204-298 3,381,157 4/1968 Ferreira 219-121 3,371,649 3/1968 Gowen 204-192 3,267,0l5 8/1968 Morley 204-192 3,210,454 8/1965 Morley 219-121 2,932,588 4/1960 Frank 117-106 2,920,002 1/ 1960 AuWarter 204-298 2,157,478 5/ 1939 Burkhardt 204-298 JOHN H. MACK, Primary Examiner S. S. KANTER, Assistant Examiner 

